The invention relates to an apparatus for drying reducing gas. The invention facilitates the drying of reducing gases at various temperature and pressure levels in a space-saving single column. The apparatus allows for the drying process, in which the water contained in the reducing gas condenses, to be carried out in stages and the condensate formed to be collected in a combined receiver without the need for pressure regulating devices. The invention also relates to a process which enables reducing gases to be dried in stages at various temperature levels.
Product gases are generated during the production of reducing gases as a result of the process. These gases contain a relatively large amount of evaporated water. Examples of reducing gases are synthesis gas, hydrogen, C3 and C4 hydrocarbons. At the end of a steam reforming process synthesis gas contains, for example, even larger quantities of water vapour, which have not been completely converted and which are present as steam at the high formation temperature of the synthesis gas. Consequently fresh synthesis gas produced in a reforming process can contain more than 25 mass percent of water vapour. In general, this is not desirable for the following processes and so the water vapour must be precipitated out of the gas. Other reducing gases also often contain water vapour. Many gases are also treated in a gas scrubbing process. Following this process water vapour is present as steam in the gas.
For this reason it is common to use processes in which gases can be dried. Drying is usually effected using a cooling process in which the water contained in the gas condenses. During this process the temperature of the gas is first lowered to normal temperature so that the majority of the water contained in the gas condenses out. In a subsequent stage, the gas can be cooled even further using a refrigerating unit so that undesirable impurities, such as methane or ammonia, can be separated out with the water. However, this process is very costly as it requires the use of a refrigerating unit and the liquid gas obtained has to be fractionated so that it can be put to subsequent use.
The temperature of the gas is often lowered gradually to normal temperature. This causes the pressure of the gas to fall accordingly. The water contained in the gas condenses gradually so that it can be dried more effectively. In the gradual cooling process, maintaining the gas flow in the process flow usually requires a complex arrangement of valves, pumps and pressure-regulating devices. In addition, it is often necessary to use several condensers and separators in series, which is costly and uses a lot of plant space.
WO 2005118466 A2 describes a process for manufacturing hydrogen which originates from synthesis gas. To this end the water-bearing synthesis gas obtained is cooled in a condenser and then fed into a second cooling system. This causes the water to condense gradually. The second cooling system is cooled using a cooling agent which is fed through a cooling reservoir, which can be embedded underground and which exploits the high thermal capacity of the surrounding subsurface. The water is then removed from the synthesis gas obtained using a water separator. Another drying device is then used to remove the remaining water traces. In this way the synthesis gas can be cooled gradually and the water largely removed.
However, the construction of the apparatus is very expensive as it requires several condensers and separators which must be connected in series, one of which may be connected to a cooling reservoir embedded underground. Consequently, the apparatus used for condensing the water requires a lot of space in itself. When implementing the process, additional cooling agent may be required to allow the gas to be condensed gradually. This is prone to problems and involves high investment costs. In addition, no indication is given as to how the gas has to be conducted to prevent it from flowing back into the separators located upstream in the process flow.
For this reason the task at hand is to make available a space-saving device which enables the temperature of a reducing gas to be gradually lowered so that the moisture contained within the gas can be gradually condensed. In so doing the pressure differences occurring must be compensated for without costly regulating devices, if possible. It should also be possible, if required, to use refrigerating machines to ensure that the water is condensed out completely. In principle, the apparatus should be able to be used for any reducing gas where it would be feasible to apply the gradual condensation process to release the water. It should also be possible to collect the condensed water in a common receiver without costly sluice devices.